A series of nanocomposite solid biopolymer electrolyte comprising of corn starch (CS) and lithium iodide (LiI) with various concentrations of nanosize aluminium oxide (Al2O3) has been prepared using standard solution casting technique. The effects of Al2O3 on the characteristics of the electrolytes are studied using Fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and differential scanning calorimetry (DSC) techniques. FTIR analysis reveals the complexation between the materials. Result from impedance measurements demonstrates that electrolyte with 2 wt. Al2O3 exhibits the highest room temperature ionic conductivity of (6.73 ± 0.78) � 10�4 S/cm. In XRD studies, the X-ray diffractogram of the highest conducting electrolyte exhibits the lowest peak intensity indicating high amorphous phase content in the sample. FESEM analysis shows that the incorporation of 2 wt. Al2O3 nanofillers develops a well distributed porous structure on the surface of CS-based film. The glass transition temperature (Tg) and melting temperature (Tm) of each sample are determined from DSC analysis. © 2021, The Polymer Society, Taipei.